I know music is not the most important part of the game, as it is merely aesthetic, and I have heard that it can be expensive to do, but as a musician here are my thoughts on the current state of Holdfast's musicians.
One flute and one drum sync together perfectly. It is wonderful. However, once you add another flute or another drum, the additional music is delayed. For the drums, it would be nice if more drums synced perfectly and increased the volume of their drumming, or perhaps change the sound file from that of one lone drum playing the song to one of multiple drums playing the same, which does sound different. For extra flutes or for the violins, it would be very much preferable to have additional harmony lines added when more join the same song; failing that, increased volume or the sound of multiple instruments playing the song would suffice.
Another thread brought this up but I would also like to see singing in this game. Not a separate singing musician unit, but simply the ability for any soldier to press his music key and sing a song while marching in single time, same as the musicians. If those could sync with the songs played by the musicians, that would be awesome. Local VOIP is an option but it doesn't seem that too many people know the words to these songs (but we could very easily learn these songs if our soldiers could sing them in-game). It wouldn't matter if it was a simple soldier's chant that changes to a louder group version when more people join, or if it sticks to the melody and harmony tracks are added, but it would be nice to put some words to the songs in a feature that doesn't add to server lag like VOIP currently does (unless you guys fixed that, hooray if you did).
As I said all of this is just aesthetic and not at all crucial to the game, but it would be lovely to see this after melee is improved, server lag spikes are eliminated, the regiment/crew system comes to fruition, and some more nations or at least more line infantry uniform variations are added.